Problem: Which of these numbers is composite? ${2,\ 11,\ 23,\ 61,\ 65}$
A composite number is a number that has more than two factors (including 1 and itself). 2, 11, 23, and 61 each have only two factors. The factors of 65 are 1, 5, 13, and 65. Thus, 65 is the composite number.